feat: expose merge strategy for configuration when automerging

[jbirch-atlassian]

Changes:

Expose the underlying merge strategy used by our platforms as a
configurable option for each repository to configure with the option
automergeStrategy. Additionally implement automergeStrategy for the
Bitbucket Cloud platform, as the only platform that doesn't currently
respect the remote repository's configured merge strategy.

Context:

closes #7184

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

How I've tested my work (please tick one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests but ran on a real repository, or
• Both unit tests + ran on a real repository

[jbirch-atlassian]

I have two areas of feedback here that I'm happy to either modify this Pull Request for, or submit in a follow-up Pull Request.

1. From an internal ergonomics perspective, I think I'd like mergeStrategy to always be required on mergePr. Then each platform would need to explicitly say what it doesn't support, instead of just "failing to know that merge strategies are a thing".
2. From a user ergonomics perspective, I think I'd like to extract the merge strategy into some form of exported function on each platform like isMergable(pr, strat) or something, so that it's possible to do a dry-run and be told "Renovate will do nothing, because platform X does not support strategy Y". At the moment, dry-run will emit what Renovate is instructed to do, and could possibly be told at runtime "It turns out platform X can't do Y".

[jbirch-atlassian]

The screenshot here, from bottom to top, shows:

• A pull request where the repository default is merge commit, and automergeStrategy was set to auto. It resulted in a merge commit.
• A pull request where the repository default is merge commit, and automergeStrategy was set to squash. It resulted in a squashed commit.
• A pull request where the repository default is merge commit, and automergeStrategy was set to rebase (unsupported by Bitbucket). It resulted in no changes between 1630639 and 3ef5842.
• A pull request where the repository default is squash, and automergeStrategy was set to auto. It resulted in a squashed commit.

Renovate commits looks like my commits because of how I ran Renovate.

[jbirch-atlassian]

I was rude and force-pushed because I noticed an error immediately after pushing, before anyone had a chance to review. The error was an incomplete list of allowedValues in lib/config/definitions.ts.

[jbirch-atlassian]

One final point of discussion: this PR is a rather in depth approach to the original ticket, with the goal of making the strategy changable on a per-renovate-configuration level, as per the discussion in #7184. However, the only strictly required change in order to resolve #7184 is just... Don't provide the optional merge_strategy parameter to the Bitbucket Cloud API.

If we don't have the appetite yet to take on exposing the merge strategy as a configuration item, I'm happy to put up those changes as a less ambitious PR instead.

Thanks again for your time and advice, y'all.

[viceice]

More later

[HonkingGoose]

Some initial changes, more to come later.

[viceice]

Please open an issue for all platforms missing implementation too.

[jbirch-atlassian]

@viceice: I'm not sure what's happening, but you're listed as "requesting changes" despite everything being resolved. I think it's coming from the changes in lib/platform/bitbucket/index.md being resolved with the suggestions in a comment, not with your suggestion.

Is everything above board, or am I just failing to GitHub today?

[viceice]

The request changes will resolve when I approve this pr.

Please open issues for the platforms which are missing this feature in this PR. After that I'll approve. 😉

[HonkingGoose]

Some things I noticed just now.

One thing is for @viceice to apply if OK, the others you can do yourself. 😉

[jbirch-atlassian]

I guess it's just I didn't know how to GitHub! Thanks for the quick education, appreciate it.

#10867, #10868, #10869, and #10870 have been created for the remaining platforms.

[viceice]

So the last small thing before we are haape to merge.

[HonkingGoose]

2 small things, looks good to me otherwise. 😉

[jbirch-atlassian]

Hey y'all, I think this one should be good to go now. I'll swing back around in a week or so and poke folk again if there's no movement.

[renovate-release]

🎉 This PR is included in version 25.60.0 🎉

The release is available on:

• GitHub release
• 25.60.0

Your semantic-release bot 📦🚀